Related Experiment Videos
A calmodulin endoproteinase from mitochondrial membranes
L S Wright1, J H Collins, K A Finn
1Department of Pediatrics, University of Wisconsin Medical School, Madison.
Abstract:
A proteinase specific for calmodulin has been identified in a crude rat kidney Triton-extracted or sonicated mitochondrial fraction and solubilized by EGTA extraction of these membranes. Mitochondrial fractions from other tissues had less activity, with relative activities: kidney = spleen greater than testes greater than liver, and no detectable activity in either brain or skeletal muscle. This enzyme is active in the presence of EGTA, but not in the presence of calcium, and cleaves calmodulin into three major peptide fragments with Mr 6000, 9000 and 10,000. N-methylated and non-methylated calmodulins were both cleaved by calmodulin proteinase and while troponin was a poor substrate, it was cleaved in the presence of either calcium or EGTA. No other EF hand calcium-binding proteins or other major mitochondrial proteins were cleaved by this enzyme. The peptides resulting from calmodulin proteinase action were isolated by reverse-phase high performance liquid chromatography (HPLC) and sequenced. Sequence analysis indicated that calmodulin proteinase cleaves calmodulin at Lys-75. The effects of proteinase inhibitors indicate that calmodulin proteinase is a trypsin-like enzyme belonging to the serine endopeptidase family of enzymes.
Insights
A novel calmodulin proteinase was found in rat kidney mitochondria. This serine endopeptidase enzyme cleaves calmodulin at Lys-75, impacting its function.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- Calmodulin is a crucial calcium-binding protein involved in cellular signaling.
- Mitochondria play vital roles in cellular energy production and signaling.
- The regulation of calmodulin activity is essential for cellular processes.
Purpose of the Study:
- To identify and characterize a novel proteinase specific for calmodulin in rat kidney mitochondria.
- To determine the substrate specificity and cleavage site of the identified calmodulin proteinase.
- To elucidate the enzymatic properties and classification of the calmodulin-cleaving enzyme.
Main Methods:
- Isolation and solubilization of mitochondrial fractions from rat kidney and other tissues.
- Enzyme assays using calmodulin and other calcium-binding proteins as substrates.
- Peptide fragment analysis using High-Performance Liquid Chromatography (HPLC) and protein sequencing.
- Characterization using proteinase inhibitors.
Main Results:
- A calmodulin-specific proteinase was identified in rat kidney mitochondrial fractions, with lower activity in spleen, testes, and liver, and none in brain or skeletal muscle.
- The enzyme is active in the presence of EGTA (ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid) but not calcium, cleaving calmodulin into three fragments.
- Sequence analysis revealed cleavage at Lys-75, and inhibitor studies classified the enzyme as a trypsin-like serine endopeptidase.
Conclusions:
- A novel serine endopeptidase, calmodulin proteinase, exists in rat kidney mitochondria.
- This enzyme specifically targets and cleaves calmodulin at Lys-75, suggesting a regulatory role.
- The enzyme's activity profile and substrate specificity indicate a unique function in mitochondrial biology.